OUCH big time Ellie-- I know exactly how that feels, did the same thing a few yrs ago and you can bet I never set foot on anything that looks "just wet". I remember laying there freezing with drizzle falling on me and the dogs going crazy and howling because I couldn't get up. A few cracked vertebrae from that experience.
I'll keep my fingers crossed that you didn't do any serious damage to that newly operated back , that would be no picnic after what you've been through.
Please keep those eyes open and your feet solidly planted until you check the conditions.